Are you surprised to see so many Japanese wearing masks in winter? Are they all sick? Actually there are many other good reasons why people wearing masks in Japan. Check it out:
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Habit, confirming to social norms, air quality, sickness.
Sometimes cold air can irritate your nose, maybe that's why, but I think it's more of a fashion trend
Its to prevent germs getting on their face in case they sneeze since during rush hour their train is packed like sardine
I think it's just a habbit
I think is a habit + culture thing. When I was in Japan, I see Japanese wear mask all the time regardless of season. Might be because some of them are sick to. It's always more polite to wear a mask when you are sick
Culture and air quality?
I am living in Japan, and have been for the past 3 years, the answer is a mixture of both culture and weather.
Weather: Cold wind makes your lips dry easily, or is extremely painful for your face in general if the cold wind directly contact your face.
Culture: When they feel that they are too lazy to put on make up (which is a thing here more so than in SG) they wear them to cover their face. (Cold winter is harder to wake up to)
because of the polition?
The air quality shouldn't be too bad in Japan. Big cities might be different though...
they are very conscious about smog on the road. and afraid of the spread of diseases since a series of deadly Avian flu.
risk of catching colds - they take very crowded public transit, and if someone is coughing, everyone is inhaling.
In China, there are a lot of winter wearing a mask, because it is anti-haze